Capacitive touch technology has found increasing utility in various applications, including mobile hand-helds, netbooks and laptop computers. Compared to other touch technologies, capacitive touch enables very sensitive response as well as features such as multi-touch. Optically clear adhesives (OCAs) are often used for bonding purposes (e.g., attachment of different display component layers) in the capacitive touch panel assembly.
Not only do OCAs provide mechanical bonding, but they also can greatly increase the optical quality of the display by eliminating air gaps that reduce brightness and contrast. The optical performance of a display can be improved by minimizing the number of internal reflecting surfaces, thus it may be desirable to remove or at least minimize the number of air gaps between optical elements in the display.
In display assembly, bonding a touch panel or display panel (such as a liquid crystal display (LCD) panel) to a three-dimensional (3D) cover glass by means of an optically clear adhesive can sometimes be challenging. Indeed, newer designs use cover glasses having a thick (approaching 50 micrometers) ink step around the perimeter or frame of the cover glass, generating a substrate that is no longer flat but is a 3-D lens. The region encompassed by the ink step is often referred to as a gap. In addition to the large ink step, other 3D features that may require good adhesive wetting of any of the display components, include things like the presence of a flex connector, slight curvature of the components, thicker ITO patterns, presence of raised integrated circuits on a touch panel and the like.
There is thus an increasing need for soft OCAs, which enable better wetting of thick inks on the display. Additionally, they can improve stress relief as a result of the display module assembly process. Such stress relieving features are particularly beneficial to reduce Mura (optical image distortion that may result from dimensional distortion) when bonding LCM and can also minimize delayed-bubble formation. A further beneficial feature of soft OCAs is short assembly cycle times.